U.S. Pat. No. 4142748, assigned to the present applicant, disclosed a privacy lock arrangement for door latch assemblies which allows an internal door latch to be snibbed on a first side to lock the latch against entry from the other side, but to be automatically released by simple rotation of the handle at the first side. Privacy Lock arrangements in general ensure privacy for the occupant of a room against unexpected entry and are widely used on bathroom, toilet and bedroom doors. The particular arrangement of U.S. Pat. No. 4142748 includes a pair of rotary members which interengage with one another so that they can rotate independently through a limited angle of rotation only. A pivoted snib member has a first dog engageable with one of the rotary members to positively lock it against rotation and a second dog which engages the other rotary member in such a way that the relative rotation of the rotary members is effective to move the snib member out of its engagement with the locked rotary member.
The arrangement of U.S. Pat. No. 4142748 has the attraction that it may be provided as an adaptor assembly between a backing plate and an escutcheon and therefore does not require modification of the handle, but is also a relatively complex mechanism to manufacture.
Earlier privacy lock arrangements are to found, for example, in U.S. Pat. No. 471190, and in British patents 861002 and 1159161.
A variation of the arrangement of U.S. Pat. No. 4142748 is disclosed in the present applicant's co-pending Australian patent application 19655192. In that case, the engagement between the releasing rotary member and the snib is by way of a lateral pin on the snib which projects parallel to the main spindle axis and is received in a V-shaped cut-out in a head portion of the rotary member.